GB2375645A

GB2375645A - Drowsiness monitor having a means for detecting a metabolic function of a user

Info

Publication number: GB2375645A
Application number: GB0103215A
Authority: GB
Inventors: Douglas Maximillian Lore Mudge
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-02-08
Filing date: 2001-02-08
Publication date: 2002-11-20
Also published as: GB0103215D0; GB2375645A8

Abstract

Apparatus for detecting drowsiness of a user 11, comprising a detector 14 for detecting the instantaneous value of a metabolic function such as heart rate or body temperature of the user 11, comparison means 15 for comparing the detected instantaneous value of the user's metabolic function with a stored value of that function representing the value in the sleeping state, and alarm indication means 16 for generating an output signal when the detected value falls below a threshold value in the vicinity of the sleeping state value. The apparatus may include a means for applying a small electric shock to alert the user of their state of awareness.

Description

APPARATUS FOR MONITORING A USERS STATE OF ALERTNESS The present invention relates to apparatus for monitoring a user's state of alertness. This has particular application in connection with users who are driving motor vehicles or operating machinery.

There have been numerous reports recently of accidents occurring as a consequence of drivers falling asleep at the wheel during long journeys and losing control of the vehicle. Although regulations are in force limiting the length of time for which the driver of a public service vehicle may drive, no such regulations are in force for private individuals and the consequences of a high speed motor accident involving private individuals is just as great.

One prior art attempt to monitor a user's state of awareness has involved optical equipment maintaining the user's eyes in its field of view and seeking to detect the rate at which the user blinks his eyelids. This is based on the theory that when the onset of sleep is imminent, individuals blink their eyelids more frequently, and consequently, detection of the blink rate can give an indication of incipient sleep onset. Unfortunately, however, people also sometimes blink more rapidly for other reasons, for example, due to foreign bodies in the eye or dazzling by low sun or oncoming vehicles and this physiological phenomenon is, therefore, unreliable for the purpose. It also involves complicated and expensive equipment and is difficult to put into practice. Furthermore, it does not take into account the fact that individuals differ in their response when sleep approaches. There are, however, some physiological or

metabolic functions such as heart rate and body temperature which are known to be different in the sleeping state from the waking state. In particular, it is known that the heart rate is lower in the sleeping state than in the waking state, and likewise the body temperature falls when the body is asleep. The present invention, therefore, proposes apparatus for detecting the transition from the state of wakefulness to the sleeping state of the user by exploiting a knowledge of these physiological or metabolic functions.

According to one aspect of the present invention, therefore, apparatus for detecting the transition from a state of wakefulness to a sleeping state of a user comprises means for detecting the instantaneous value of a metabolic or physiological function of the user, means from comparing the detected instantaneous value of the metabolic or physiological function with the stored value of that function in the sleeping state, and a means for generating an output signal when the detected value falls below a threshold value in the vicinity of the said sleeping value.

As mentioned above, the physiological or metabolic function may be the heartbeat rate. This is a function of the human body which is well defined and relatively easy to detect. Indeed, equipment for detecting and displaying the heartbeat rate is already commercially available for sportsmen who have an interest in their heart rate for training purposes.

Alternatively, or additionally, the physiological or metabolic function may be the body temperature, and again instruments for measuring temperature are well known

and can be incorporated into the apparatus of the invention without difficulty.

The output signal generated by the apparatus of the invention may be an output alarm signal simply for the purpose of alerting the user to the incipient sleep state, and such an alarm signal may be an audible alarm or a visible alarm. Both have the advantage that they can be perceived by others in the vicinity so that, in the postulated example of a driver of a motor vehicle, any passengers can also be alerted to the incipient sleep-state of the driver and can take appropriate action. Of course, the apparatus of the present invention is not applicable solely to drivers of motor vehicles, but may also be used by anyone for whom a sleep-state would be unwelcome or dangerous, for example, students working late into the evening in preparation for examinations may wish to avoid falling asleep at their desks as a matter of convenience, whereas operators in charge of dangerous machinery may find it of value to have an alertness indicator so that, for example, their supervisor can withdraw them from their duties if their alertness state falls below that which is required for safe operation of the machinery.

The manner in which the sleep onset condition is detected may, of course, involve the sensing of more than one physiological or metabolic function in order to gain certainty, and apparatus may be formed in accordance with the invention which is provided with means for detecting the value of two metabolic functions, in which the means for comparing the alert-state and sleeping-state values is operable to trigger the output signal only when both detected instantaneous values pass the said threshold values. Anomalous conditions of one physiological of metabolic function are thus

screened from triggering spurious output signals.

As well as, or as an alternative to the provision of an alarm output signal, the apparatus of the present invention may be provided with means for applying an electric potential difference between two spaced locations on the skin of the user. By appropriate choice of the voltage this can give rise to a'tingling'sensation or a small electric shock sufficient to alert the user to his or her state of awareness.

Likewise, the output signal may be in a different form from a simple alarm signal, for example it may be used to control the machinery itself in circumstances where this would not of itself be dangerous. For example, a machine operator approaching a somnolent state may trigger the machinery to cease functioning so that the danger to the user of the sleep-state is effectively removed. In its embodiment suitable for a motor vehicle driver, the sensor may be portable, for example carried on a wrist for detecting the pulse of the user. A chest mounted sensor may also be used for additional security as this can more readily detect the heart beat.

The present invention also comprehends a method of monitoring the state of alertness of a user comprising the steps of detecting the value of at least one physiological or metabolic function when the user is in a sleep-state, storing the value of the said physiological or metabolic function and comparing it with the instantaneous value of that function as detected by a sensor in use of the apparatus, and utilising the result of the comparison to determine when the user is approaching a sleeping state. The method of invention may further include the step of generating an output signal when

an approaching sleep-state is detected in order to alert the user to this fact.

Various embodiments of the present invention will now be more particularly described by way of example, with reference to the accompanying drawings, in which; Figure 1 is a schematic view of a driver in position in a motor vehicle and wearing a sleep monitor formed as an embodiment of the present invention; Figure 2 is a schematic view of an alternative embodiment of the invention; and Figure 3 is a block schematic diagram of the embodiment of Figure 2.

Referring first to Figure 1 there is shown a driver generally indicated 11 in charge of a motor vehicle 12. In this embodiment that driver 11 is wearing a chest strap 13 bearing a heart beat sensor 14 which detects the heart beat by analysing the acoustic signals, and transmits a radio signal to a wrist-worn discriminator 15 in which is stored the driver's sleeping heart rate. If the signal from the sensor 14 indicates that the heart rate at the time is approaching the sleeping heart rate it generates an output signal to an alarm unit 16 which flashes to alert the driver 11 to the incipient sleepstate, and at the same time issues an audible warning detectable by any other passengers in the vehicle 12.

An alternative embodiment is illustrated in Figure 2, which is an entirely wrist-worn unit capable of detecting both the heart rate and the user's temperature. This device comprises a body 17 having a wrist strap in two parts 18 and 19, one of which carries

a buckle 20 for engagement with a co-operating element 21 on the other. This other wrist strap part 19 carries a temperature sensor 22 and a microphone 23 both of which are connected by conductors (not shown) embedded within the strap 19 and insulated from one another and from the outside, lending to a discriminator and alarm unit 10 housed in a casing 17.

On the casing 17 is an indicator lamp 24 (such as a light emitting diode) and an acoustic indicator or loud speaker 25. In this embodiment both the temperature of the skin of the wearer when sleeping, and the sleeping heart rate are preliminarily detected and stored in a memory (not shown) within the body of the instrument 17.

In use, then, if the pulse rate should vary, for anomalous reasons, without the skin temperature also falling to indicate the onset of sleep, the apparatus will not produce the output alarm signal or illuminate the warning lamp, it being necessary for both physiological functions to indicate an incipient sleep-state before the alarm indication is generated.

The operation of the instruments shown in Figure 2 is illustrated in more detail in Figure 3, which shows the temperature sensor 22 and the pulse rate sensor 23 as the input units to the system.

It will be appreciated that a system of this type is battery operated, and the battery and associated circuitry, including circuitry for monitoring the state of the battery and for indicating when the battery is low, are not shown since these are all conventional components and do not form part of the present invention.

The output from the temperature sensor 22 is fed to an analogue-to-digital converter 28 which converts the analogue signal from the temperature sensor 22 into a digital signal which is then supplied to a comparator 29. The other input to the comparator 29 is supplied by a memory 30 which stores the digital value of the skin temperature of the user at sleep. This is stored in a preliminary calibration step. The comparator 29 produces an output signal when the digital signal from the analogue-to-digital convertor 28 is less than or equal to a threshold value determined to be just above the sleeping value of skin temperature stored in the memory 30. This can be achieved either by providing the comparator 29 with a small offset or by storing in the memory 30 a value comprising the sleeping temperature increased by a small increment to account for this offset. When, in use, the skin temperature falls to this threshold value the comparator 29 generates an output signal on a line 31 which leads to a coincidence circuit 32, which may be a simple AND gate.

The other input to the AND gate 32 is fed by a channel leading from the pulse rate sensor 23. This may be a pressure sensor positioned over a vein in the wrist, or an acoustic sensor capable of detecting the acoustic variations in the sound from the wrist due to the repeating pulse. Obviously noise-reduction and discrimination circuits are required for the regular pulse signal to be extracted from all other sounds which would be detected by sensor 23 but not separately shown, and these are incorporated in the sensor 23. The output from the signal 23 is fed to a pulse shaper which produces at its output a square wave signal at the frequency of the pulse. This is then applied to a counter 34. The'reset'input of the counter 34 receives a signal from a

clock 35 which determines the time period over which the pulse is counted. This interval is, in practice, determined by the frequency of the heart beat signal and the required level of monitoring. For example, a typical heart rate may vary between 62 and 95 beats per minute and in a non-critical situation the timer 35 may generate an output signal once every minute so that the output from the counter 34 will represent numerically the heart rate in beats per minute. For use as a driving safety device, however, an output signal once every minute may be too infrequent and a signal once every five or ten seconds may be more appropriate. However, since the pulse monitor is detecting individual pulses, a reset every five seconds would allow only five whole pulses to be received at a heart rate of 60-69 beats per minutes and only seven whole pulses to be received at a pulse rate of 95 beats per minute. The shorter reset interval therefore involves a less precise sensitivity of the instrument.

The output from the counter 34 is sent to a sample and hold circuit 35 which maintains the last whole number of pulses counted before the counter was reset, and this generates an output signal to a frequency comparison circuit 36, the other input from which is received from a memory 37 which stores the threshold value of the pulse rate established from the preliminarily calibration operation. Again, as discussed with reference to the temperature sensor, the memory 37 may store the sleeping pulse rate increased by a safety margin to provide a threshold value at which it is considered that sleep onset is imminent.

The output from the frequency comparison circuit 36 is generated, therefore, when the number on the line from the sample and hold circuit 35 is equal to or less than the

number arriving from the memory 37, and the output from the frequency comparison circuit 36 is supplied to the AND circuit 32. When this detects both inputs at a high level it passes a signal to a power circuit for generation of an alarm signal to the acoustic indicator 25 and the light emitting diode 24. The power circuit also applies a signal to two electrodes 26,27 on the back of the unit 17, which generates a potential difference between them and, therefore, across two points on the skin of the user to provide a'tingling'or slight electric shock to alert the user to the incipient sleep-state. The light emitting diode display may be, for example, a red disc in the region of the size of a watch face.

Claims

1. Apparatus for detecting the transition from a state of wakefulness to sleepstate of a user, comprising means for detecting the instantaneous value of a metabolic function of the user, means for comparing the detected instantaneous value of the metabolic function with a stored value of that function in the sleeping state, and means for generating an output signal when the detected value falls below a threshold value in the vicinity of the said sleeping value.

2. Apparatus as claimed in Claim 1, in which the said metabolic function is the heartbeat rate.

3. Apparatus as claimed in Claim 1, in which the said metabolic function is the body temperature.

4. Apparatus as claimed in any of Claim 1 to 3, in which the output signal is an output alarm signal.

5. Apparatus as claimed in Claim 4, in which the output alarm signal is an audible alarm.

6. Apparatus as claimed in any of Claims 2 to 6, in which the output alarm signal is a visible alarm.

7. Apparatus as claimed in any of Claims 2 to 6, in which there are provided means for detecting the value of both metabolic functions and the means for comparing values is operable to trigger the output signal only when both detected instantaneous values pan the said threshold values.

8. Apparatus as claimed in any preceding claim, further including means for applying an electric potential difference between two spaced locations on the skin of the user.

9. Apparatus as claimed in any preceding claim, in which the sensor is carried on a wrist strap for detecting the pulse of the user. [or may be a chest strap]

10. A method of monitoring the state of alertness of a user, comprising the steps of detecting the value of at least one metabolic function when the user is in a sleepstate, storing the value of the said metabolic function and comparing it with the instantaneous value of that function detected by a sensor and using the result of the comparison to determine when the user is approaching a sleep-state.

11. A method as claimed in Claim 10, further including the step of generating an output signal when an approaching sleep-state is detected in order to alert the user to this.

12. A method as claimed in Claim 10 or Claim 11, in which the apparatus also generates an output audible signal or visual signal to alert any person in the vicinity

of the user to the approaching sleep-state thereof.

13. Apparatus for monitoring a metabolic function substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

14. A method of detecting the transition from wakefulness to a sleep-state substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.